Thus far, there is one major caveat for prospective buyers: Mad Moxxi tends toward the higher end of the difficulty spectrum, especially while flying solo. It's a good thing that you can re-spec your character at any time, since you'll need to reallocate your skill points in areas that restore health and shields wherever possible. Enemies don't drop health or ammo when killed; instead, supply drops occur between waves, though you only have seconds to gather as much health and ammo as you can. This made life particularly difficult playing as a Level 30 Siren, as a few abortive attempts at Hell-Burbia forced me to place a new emphasis on abilities that recharged my shield after kills and recharged my health during phasewalks. It's extremely important that you survive, as dying (actually dying, not falling and getting a second wind) instantly starts an entire arena sequence over. All of your round and wave progress is lost if you're playing alone and die; in multiplayer, players who fall without being revived are sent to a penalty box, where they can shoot, but can't leave.

The weird thing is that battling in the arenas doesn't award you experience -- nor weapons. Though the rewards might be delicious if you make your way to the end of an arena (I'm not sure, my poor Level 11 could never get that far), it robs Underdome fights of the feeling of constant character growth, which is really the driving force behind Borderlands. (Update: Gearbox tells us that new weapons drop underneath Moxxi after each round but "the XP thing is intentional after a lot of focus testing. It breaks the rest of the game if you let people crank up too much XP. This is a separate game mode.")

The atmosphere helps sell the spectacle; an unseen crowd cheers you on and makes you feel like you're on a deranged game show, and when you're the last player alive (i.e. not in the penalty box), the crowd begins to chant your name. The gritty electronica that plays in the background is the first memorable music the game has offered, and fits the frenetic pace. Finally, in a game full of insane characters, Moxxi is perhaps the looniest of them all, constantly cheering for/belittling your efforts, stoking the crowd, and laughing in a manner that can only be described as erotic. In other words, it's just another day in the Borderlands...